Large Benthic Foraminifers Research Articles

Cenomanian–Turonian facies succession in the Guerrero–Morelos Basin, Southern Mexico

The Cenomanian–Turonian succession of southern Mexico is characterized by an abrupt change from shallow marine to pelagic facies. The drowning of the platform coincides with the widely documented Cenomanian–Turonian Oceanic Anoxic Event (CTOAE). A proper understanding of the drowning event and the effects of the OAE requires, as an essential first step, the construction of a detailed stratigraphic framework. This has been achieved and utilizes sedimentological data as well as a combination of benthic and planktonic biostratigraphic schemes. Deposition of the Cenomanian–Turonian sedimentary rocks of the Guerrero–Morelos basin was controlled by tectonic and oceanographic factors resulting in depositional environments ranging from a semi-restricted shelf, ramp, pelagic and prodelta deposits. Facies analysis indicates that shallow marine limestones of the Morelos Formation (lower-upper Cenomanian) were deposited in intertidal–shallow supratidal and subtidal environments in a semi-restricted shelf. Peloidal-bioclastic packstone–wackestones with minor grainstones are the predominant texture of these rocks. Abundant large benthic foraminifers, calcareous algae (dasycladacean) and mollusks (gastropods and rudists) characterize the fossil assemblage. The Cuautla Formation (uppermost Cenomanian–Turonian) represents sedimentation on a low-energy, wave-dominated, carbonate ramp. The inner ramp accumulated bioclastic banks and shoals composed of peloidal-benthic foraminifer-grainstone, calcareous red and green algae, rudists and minor solitary corals. The middle ramp is represented by nodular packstones with a diverse assemblage of echinoderms, green and red algae, bryozoan, rudists, solitary corals, roveacrinids, calcisphaerulids, and non-keeled planktonic foraminifers. The outer ramp is dominated by argillaceous wackestone–packstone characterized by calcisphaerulids, roveacrinids, and non-keeled planktonic foraminifers. An increase in terrigenous-clastic material towards the eastern part of the area indicates progradation of a deltaic system while the Mexcala Formation (uppermost Cenomanian–Turonian) was deposited in a pelagic setting. The drowning of the platform is at the contact between the Morelos and Cuautla or Mexcala formations and is dated as latest Cenomanian. The drowning is a hiatus in most sections and it began before the end of the Cenomanian by a minimum of 150 ky if the top of the Morelos is not eroded.

Conicopfenderina ? balkanica n. sp. (grand foraminifère benthique), nouveau marqueur du Valanginien des Balkanides (marge nord-téthysienne, Bulgarie)

Conicopfenderina ? balkanica n. sp. (larger benthic Foraminifera), new index-species of the Valanginian from Balkanides (North-Tethyan margin, Bulgaria). Description of a new species of Pfenderinidae (streptospiral, then rectilinear, larger benthic foraminifer with a keriothecal wall), Conicopfenderina ? balkanica n. sp.. This orbitolinid-like high-sized new taxon is observed in abundance within the internal/proximal shelf limestones of the Slivnitsa Formation (Western Balkan, Bulgaria). On the East-European part of the North-Tethyan margin, this foraminifer appears to constitute a good index of the Valdanchella miliani zone (rather Upper Valanginian in age). Until now, such a biostratigraphic subdivision was thought to be paleobiogeographically restricted to the « Catalan sub-province », linking, on the same margin but more to the west, Jura to Iberian Range. To cite this article: B. Peybernès, C. R. Palevol 3 (2003).

Provenance analysis of Oligocene autochthonous and allochthonous coralline algae: a quantitative approach towards reconstructing transported assemblages

The Oligocene shallow-water carbonates of the Lower Inn Valley (Tyrol, Northern Calcareous Alps) contain a rich coralline algal flora. These carbonates are known from two distinct settings: (1) autochthonous limestones and (2) debris flows intercalated with deeper water marls. The carbonate facies are dominated not only by crustose coralline algae (Corallinaceae, Rhodophyta), but also by smaller and larger benthic foraminifers, bryozoans, corals as well as lithoclasts of Triassic origin. Five species of coralline algae are identified and described in detail: Lithoporella melobesioides, Lithothamnion sp. A, Lithothamnion sp. B, Mesophyllum sp., and Sporolithon sp. The distribution of algal taxa shows distinct relationships to non-algal biota and substrates: L. melobesioides preferably encrusts other coralline algae, Lithothamnion sp. A is found encrusting bryozoans, Lithothamnion sp. B encrusts corals, while Mesophyllum sp. grows directly on fine-grained, soft substrates. Besides the fact that algal taxa reveal close relationships to other components, it can also be shown that algal assemblages are highly correlated to carbonate facies types. Hierarchical cluster analysis based on the relative abundance of taxa reveals five coralline algal assemblages showing distinct distribution patterns among carbonate facies. While two of the assemblages are restricted to the debris flows, the other three were found in both debris flows and autochthonous occurrences. A correlation between algal assemblages and carbonate facies allows the following conclusions to be made: (1) Both coralline algal taxa in particular and algal assemblages as a whole show distinct relations to water depth (herein referred to as a summary of light conditions and hydrodynamic energy) and substrate relationships. This makes them potentially valuable indicators for palaeoecological reconstructions. (2) Most of the coralline algal assemblages in allochthonous occurrences (i.e. debris flow) can be traced back to facies patterns in autochthonous occurrences. This indicates that a thorough microfacies analysis combined with a systematic study of specific components can be very useful in the reconstruction of palaeoenvironments, even if these are not preserved in their original context. (3) Some of the coralline algal assemblages within debris flows cannot be traced to autochthonous facies and do not seem to reflect primary facies compositions as they contain an atypical mixture of algal taxa and other components. These are characterised by a relatively high abundance of lithoclasts (usually >20% of the components) and a high degree of fragmentation of coralline algae thalli.

Biostratigraphy and environmental changes across the Cenomanian–Turonian boundary, southern Mexico

Integrated benthic and planktonic foraminiferal biostratigraphy has been used to correlate sections that include the transition from upper Cenomanian shallow-marine facies to lower-middle Turonian pelagic facies in southern Mexico. The Cenomanian shallow-marine, semi-restricted limestones lack planktonic foraminifers, while the Turonian pelagic limestones are almost devoid of benthic fauna. The Pseudorhapydionina dubia, Whiteinella archaeocretacea, and Helvetoglobotruncana helvetica zones have been characterised in this interval. The disappearance of the zonal marker and of most benthic foraminifers defines the top of the P. dubia zone. The W. archaeocretacea zone comprises the transition from shallow semi-restricted conditions to open-marine, deeper environments. A characteristic of this zone is the scarcity of both benthic and planktonic foraminifers, including the zonal marker. The top of this zone is marked by the first appearance of H. helvetica. Some changes in the fossil assemblages reflect the successive stages of the drowning of the platform. Others seem to be linked to global factors and have potential for wider correlations. The Cenomanian platform had its maximum development in the P. dubia zone. Adverse conditions for carbonate producers (and for platform growth) started in the latest Cenomanian, when extensive areas of the platform underwent subaerial exposure. Habitat reduction might have been an important factor for the extinction of most large benthic foraminifers at the end of the P. dubia zone. The change to deeper open marine conditions with the subsequent relative sea-level rise could have delivered the final blow to those groups that survived the habitat reduction. These organisms did not survive for long into the W. archaeocretacea zone. Some areas deepened to pelagic conditions after a short period of grainstone deposition in which molluscs were the dominant bioclasts. In the areas where shallow-marine deposition continued, a sharp increase in algal remains indicates higher nutrient levels and mesotrophic conditions. Fully eutrophic conditions are represented in overlying facies dominated by echinoids, calcisphaerulids, and roveacrinids. This degradation of the environment further abated carbonate production and contributed to the drowning of the whole platform.

Autochthonous facies and allochthonous debris flows compared: Early oligocene carbonate facies patterns of the Lower Inn Valley (Tyrol, Austria)

This study presents a microfacies analysis and palaco-environmental interpretations of Early Oligocene carbon ates from the Lower Inn Valley Tertiary (“Unterinntal-Tertiar”) of Austria. The well preserved biogenic components allow detailed investigations of component relationships and controlling ecological parameters. The carbonates are dominated by coralline algae, corals, small and large benthic foraminifers, bryozoans and lithoclasts. Bivalves, gastropods, echinoderms, brachiopods and serpulids are subordinate. The limestones are present as A) autochthonous carbonates transgressing directly above the Triassic basement and B) allochthonous debris flows within deeper-water marls. These carbonates are found within the Paisslberg Formation. The Werlberg Member within this formation, pertains to the autochthonous carbonates and larger debris flows.

Microtaphofacies of a Warm-Temperate Carbonate Ramp (Uppermost Tortonian/Lowermost Messinian, Southern Spain)

The combined analysis of the sedimentary structures, internal depositional geometries, and microfacies of uppermost Tortonian/lowermost Messinian shallow-marine carbonates (Agua Amarga Basin, southern Spain) has aided in unraveling the geological record of a highly dynamic ramp environment. The biogenic BRYOMOL association with large benthic foraminifers inhabited a warm, temperate climate (17-20 degrees C). Sediment distribution was governed by physical parameters, and redistribution and mixing of particles blurred original biogenic zonations. Thus, although the carbonate factory can be localized on the mid ramp based upon sedimentary structures and depositional textures, sediment composition is quite uniform over the depositional profile, and only qualitative paleontological evidence exists for the original presence of seagrass patches (benthic foraminifers, biomuration fabrics in bryozoans). Originally aragonitic biota (i.e., molluscs), quantitatively important in all Cenozoic shallow-marine environments, were dissolved during or soon after deposition and left no significant trace in the fossil record. Consequently, the diagenetic potential of the sediments was low, and the deposits remained essentially unlithified for a long period. During lowstands and transgressions, particles were partly reworked from previously deposited material. Sediment compositions within these units are increasingly biased toward concentrations of mechanically more resistant carbonate grains as a function of many deposition and exhumation cycles. In line with taphonomic experiments, nodular (celle-poriform) bryozoans disappear before robust and delicate branching bryozoans. Resistant grains include echinoderm ossicles, bivalve shell materials (calcitic), foraminifers, balanids, and non-carbonate particles. The quantitative proportions of these grains have been used to define microta-phofacies (new term). Particle and, therefore, sequence dynamics of temperate carbonate-ramp systems resemble these in siliciclastic environments, and challenge the classic concept of (tropical) carbonate sequence stratigraphy. Careful microfacies analysis of temperate skeletal carbonate depositional systems and depositional sequences provides an important additional tool in further understanding the architecture of bioclastic carbonate bodies in the subsurface.

Cool-water carbonates in an Eocene palaeoestuary, Norseman Formation, Western Australia

Numerous palaeovalleys formed extensive drowned estuaries during Eocene transgressions along the southwestern part of the southern margin of Australia. The Tertiary sediments of the Cowan palaeovalley have been extensively drilled, revealing deposition of the Norseman Formation during the Middle Eocene Tortachilla transgression. Initial deposition occurred during transgression of the valley to form a drowned estuary. Sediments consisted of coarse-grained muddy, lithic, iron and glauconite-rich sands and gravels of mixed carbonate and quartz. Pure carbonates accumulated during the highstand, produced by a typical shallow temperate water assemblage of bryozoans, coralline algae, echinoids and molluscs and were swept into shoals by strong tidal currents. Minor “tropical” components in the form of large benthic foraminifers and dasycladacean algae are present. Coarse bryozoan and trough cross-bedded carbonate sands accumulated in the margins of the estuary and fine bryozoan sands in the deeper parts. Rhodoliths accumulated to form shoals in sheltered localities. The Spencer Gulf and Gulf St. Vincent of South Australia provide close modern analogues to the Cowan palaeovalley and the Norseman Formation. Modern carbonate sediments off Esperance on the south coast of Western Australia contain “tropical” faunal elements within an otherwise temperate skeletal assemblage and also provide a modern analogue. The Norseman Formation thus provides an excellent example of cool-water carbonate deposition in near-shore, tide-dominated environments. This study complements and contrasts existing cool-water shelf facies models based on Tertiary carbonates deposited on deep shelves elsewhere in southern Australia.

Unusual faunal associations during Upper Cenomanian-Lower Turonian floodings on the Niger ramp (central West Africa)

Abstract The Upper Cenomanian-Lower Turonian marine deposits of the Iullemmeden Basin and of the northern Chad Basin (Niger) consist of interbedded mudshales and fossil-rich limestones that formed on a ramp as a result of a Tethyan transgression. The faunal content of the limestone beds is characterized by (1) the absence of forms typically found on the Tethyan platforms: rudistids, corals and commonly associated forms (large benthic foraminifers, bryozoans, calcareous sponges, red and green algae); (2) the absence of pycnodonts and of brachiopods, and (3) the abundance of Gryphaeidae and Ostreidae, as well as the relative abundance of ammonites. This unusual faunal composition is ascribed to several factors. Rudistids, corals and associated forms may have failed to occur because of the general decrease in the diversity of these organisms in the Upper Cenomanian-Lower Turonian and because of the lack of suitable shoals on the Niger ramp for reefs to develop. Pycnodonts may have failed to gain a foothold in the face of severe competition from pioneer and opportunistic bivalves (Gryphaeidae, Ostreidae) that quickly colonized the ramp. The absence of brachiopods has not yet been explained satisfactorily; it could be due to several factors, including severe competition with pioneer bivalves and/or excessive turbidity of bottom waters.

869. Vacuum furnace for high temperature diffusion anneals: N.L. Peterson and R.E. Ogilvie, Rev. Sci. Instrum., 34 (2), Feb. 1963, 193–194

The paleontological investigations of the Jurassic of Western Thailand, districts of Mae Sot (Tak–Mae Sot highway, Padaeng Tak and Ban Mae Kut Luang Zinc mines) and Umphang (Klo Tho), provide age constraints for the Late Indosinian orogeny, the Paleotethys closure and the timing of the marine Jurassic inundation of Sundaland. The basal conglomerate of the Jurassic is derived from the pelagic Triassic Mae Sariang substratum. Stratigraphy, microfacies and paleontology of the Jurassic marine strata focus especially on ammonites, bivalves, large benthic foraminifera and algae. Among ammonites, the Tethyan Catulloceras perisphinctoides Gemmellaro marks the Upper Toarcian (Aalensis Zone) along the Tak–Mae Sot highway and Riccardiceras longalvum (Vacek), Malladaites pertinax (Vacek), Abbasites sp. and Vacekia sp. indicate Middle Aalenian to lowermost Bajocian in the Padaeng Mine (SE of Mae Sot) and Klo–Tho (Umphang). Vacekia sp., Spinammatoceras schindewolfi Linares and Sandoval and Malladaites vaceki Linares and Sandoval indicate Middle Aalenian to lowermost Upper Aalenian at Ban Mae Kut Luang (NE of Mae Sot). Among foraminifers, the large benthic foraminifer Timidonella sarda Bassoullet, Chabrier and Fourcade in the Western Tethys is indicative for Aalenian–Bajocian times, as characterized in the section at the Tak–Padaeng Zinc mine and the Klo–Tho Formation near Umphang. The endemic foraminifer Gutnicella kaempferi characterizes the Pu Khloe Khi Formation near Umphang. Among bivalves, shallow marine, dominantly endemic fauna includes Parvamussium donaiense (Mansuy) and Bositra ornate (Quenstedt), from the Toarcian to the Early Bajocian. A consideration of the faunal affinity shows that the fauna is partly endemic with Northern Tethyan (Eurasian) affinity.